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June 15, 2011 -- Sleep-deprived people have trouble reading facial expressions, a new study shows, particularly when those faces are shifting away from anger or threat.

The finding suggests that sleepy people may have impaired judgment, especially in situations where they are dealing with an angry or threatening person who is backing down.

The study was presented at the annual meeting of the American Academy of Sleep Medicine and the Sleep Research Society in Minneapolis.

Tracking the Effects of Sleep on Emotional IQ

Researchers at the University of California at Berkeley scanned the brains of 12 healthy young adults as they watched a computer-generated face.

Investigators used computer software to tweak the face’s features slightly, with the lift of an eyebrow here or the flare of a nostril there, to display a gradient of emotion as it moved from either very threatening to neutral or friendly to neutral.

Study volunteers were asked to rate each of the 70 images in a series as being either threatening or nonthreatening, or friendly or not friendly.

When the participants were well rested, they had no trouble picking up on the emotional changes, but when they were deprived of sleep after 24 hours, that ability was impaired.

“As the pictures start to get less and less threatening, the people who are sleep deprived continue to rate them as threatening,” says study researcher Matthew P. Walker, PhD, director of the Sleep and Neuroimaging Laboratory and associate professor of psychology at UC Berkeley.

The ability to sense emotional shifts in friendly faces didn’t appear to be affected.

Social and Professional Consequences

“Facial expressions are probably the most salient cues that we have in our environment,” Walker says. “They profoundly influence how we behave, and they can rapidly alter your feelings and your actions toward other people.”

He says not sleeping enough could have profound social and professional consequences, particularly for people like doctors, police officers, or soldiers, who are frequently called on to quickly assess and respond to interpersonal situations.

“We’re social animals. If we have problems with recognition of emotional cues, we get in trouble with other people,” says Marlene Oscar Berman, PhD, professor of neurology and psychiatry at the Boston University School of Medicine.

Berman studies emotional recognition in the brains of former alcoholics.

She’s found that past alcohol abuse, like sleep deprivation, appears to impair the ability to recognize emotions in the faces of other people.

Berman thinks damage to an area of the brain called the amygdala, a region important for memory, attention, and decision making, may be causing the problem.

People who can’t accurately recognize emotion, she says, often struggle in life.

“Emotional recognition is tied to the recognition of positive and negative feedback in general, and that gets into the whole area of decision making,” she says. “If you can’t make good decisions, you can get into big trouble.”

This study was presented at a medical conference. The findings should be considered preliminary because they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

SOURCES:Annual meeting of the American Academy of Sleep Medicine and the Sleep Research Society, Minneapolis, June 11-15, 2011.Matthew P. Walker, PhD, director, Sleep and Neuroimaging Laboratory; associate professor of psychology, University of California, Berkeley.Marlene Oscar Berman, PhD, professor of neurology and psychiatry, Boston University School of Medicine.